Overload relay



Jan. 23, 1934. G wlLMS Re. 19,062

OVERLOAD RELAY Original Filed Aug. 8, 1928 v 2 Sheets-Sheet 1 @Maaw Jan.23, 1934. G, W LM Re. 19,062

OVERLOAD RELAY Original Filed Aug. 8, 1928 2 Shets-Sheet 2 Qfi/wdeewof/ENEMY L7. H/z]1775 WWW e m ig Reissued Jan. 23', l9 34 UNITED. STATESOVERLOAD RELAY Gustav 0. Wilms, Milwaukee, Wisl, assi'g'nor, by. mesneassignments, to Allen-Bradley pompany, Milwaukee, Wis., a corporation ofWlSCODSlIl Qriginal No. 1,844,491, dated February 9, 1932' Serial No.298,300, August 8, 1928. Application. for reissue October 30, 1933.

1 Claim.

ject the'improvement of the efliciency of .such relays.

Thermal relays'heretofore in use have func-' tioned satisfactorily wherethe operating overload has been suliiciently high asapproximately 600%but their slow response when used with such relatively smallerover-loads as 100 to 150% due to the temperature rise beinginsufficient, has been extremely objectionable and this invention,

16 therefore, contemplates as an object the provision of an-improvedthermal over-load relay embodying a heating element, the characteristicof which is such that its resistance increases rapidly as itstemperature rises thus insuring the desired quick operation of the relayupon the occurrence of over-loads of lesserdegree than that heretoforeoperated with.

Another object. of this invention resides in the provision of animproved over-load relay of the character described in which the heatingelement is formed of iron or any other material having a marked positivetemperature coefficient whereby its resistance rapidly. increases as itstemperature rises;

A further object of this invention resides in the provision of animproved over-load relay of the character described which may be readilyreset in a relatively short time after the over-load occurs. I

And a still further object of this invention resides in the provision ofan improved over-load relay of the character described which may beconveniently enclosed in a suitablehousing and which has means actuatedfrom the exterior of the housing for resetting the device.

With the above and other objects in view which will appear as thedescription proceeds, my invention resides in the novel construction,combination and arrangement of parts substantially as hereinafterdescribed and more particularly defined by the appended claim, it beingunderstood that such changes in the precise embodiment of thehereindisclosed invention may be made as come within the scope of theclaim.

In the accompanying drawings, I have illustrated one complete example ofthe physical embodiment of. my invention constructed according to thebest mode I have so far devised for the practical application of theprinciples thereof, and in which:

Serial No. 695,938

This invention relates particularly to an over- Figure 1 is a front planview of my improved over-load relay shown with the cover of itsenclosing housing removed;

Figure 2 is -a sectional view taken through Figure 1 on the plane of theline 2-2;

Figure 3 is a fragmentary top plan view of the over-load relay removedfrom its housing and with a' portion thereof broken away to more clearlyillustrate structural details;

Figure 4 is an enlarged side view of the overload relay shown detachedfrom the housing and its mounting panel with parts thereof broken awayand in section;

Figure 5 is a diagrammatic view illustrating my improved relayincorporated in a simple motor circuit, and t Figure 6 is a diagrammaticview illustrating the over-load relay as applied to a three phasestarting system for motor l Referring now more particularly to theaccompanying drawings, in which like numerals represent like partsthroughout the several views, 5 designates a housing stamped frombendable metal or otherwise formed in which a base of insulatingmaterial 6 is suitably mounted and hav- 8o ing its interior partiallylined with insulating material 7 The mechanism of the over-load relay ismounted on the base 6 and is carried by a bracket member 3 havinga-vertical attaching portion '9 by which it is secured to the base 6.From the upper end of the portion 9 the bracket is directed laterally,as at 10, and then upwardly, as at 11, and back again in a planeparallel to the part 10, as at .12, forming substantially a-U shapedstructure, the part 12 being shorter than the part 10. As illustrated inFigures 2 and 3, the vertical attaching portion 9 is of less width thanthat of the remainder of the bracket and the part 10is reduced inwardlytoward the narrower width of the member 9.

The bracket 8 is mounted medially on the base 6 and substantially in.line with the upper part 12 thereof and carried by the base 6 is aswitch member 13. The switch .member 13 constitutes the movable elementof a disconnecting or circuit breaking switch and is formed of a stripof yield able conducting material having a contact 14 secured to itsouter end and having its inner end bent back in substantially hairpinfashion to be 105 impinged between the adjacent portion of the base 6and one leg of a substantially U shaped terminal 15. A screw 16 passingthrough an aperture in the base 6 is threaded in the leg of the erminal15 to connect the same therewith'and I V the opposite leg or theterminal isprovided a switch member 13.

I The m'ovable contact 14 cooperates with a stationary or fixed contact19 secured on the base 8 by a screw 20 passing through an aperture inthe base and threaded in the terminal, arcshields 21 being provided ateach side of the contacts as is customary. The contact 19 is connectedto a magnetic blow-out coil 23, one 'end or which is .connected with thecontact 19 at its attachingscrew 20 and the other end with a terminal24, at the back ofthe insulating base 6 by a conductor, not shown. Oneend of a coil of resistance wire forming a heating element 25 is securedto the terminal 24 and the other to a-terminal 26 connected with aterminal 27 at theback of the base 6 by a conductor. not shown, withwhich the end of the lead 22 is connected.

The switch arm 13 is held in its position closing the switch by themechanism of the relay now about to be described. The part 10 of thebracket 8 is provided with a threaded aperture 28 in which a bushing 29formed of suitable heat resisting refractory material is looselythreaded, and the space therebetween being filled with a suitable heatresisting cement 30. The cement 30 also fills a space left betweentheflange 31 of the bushing 29 and the upperface of the part 10 andencircles the flange to secure the bushing onto the part 10. I

A substantially cup-shaped washer 32 is positioned above the flange 31of the bushing and is secured thereto by like cement 30, the bushingbeing apertured, as at 33, and having a hollow stem 34 secured in itsaperture with its major portion extending below the part 10 of theybracket and its top portion extending through the aperture of the washer32 to mount a ratchet 35.

The ratchet 35 has a'downwardly projecting annular boss or flange 36 ofa diameter slightly less than the diameter 01 the recess 3'7 in thewasher 32 and the diameter of its opening is slightly greater than theoutside diametervoi the stem 34. Solder 38 or other metal of relativelylow melting point fills the space between the stem-34 and the apertureof. the ratchet and the recess 37 of the washer to normally secure theratchet 35 to the stem 34. The heating element or coil 25 is wound aboutthe downwardlyprojected portion 01 the stem 34 in close thermal relationthereto so that when an over-load occurs its heat, due to the excessivecurrent pass- .ing therethrough, is conducted to the metal 38 whichmelts and frees the ratchet. This freeing of the ratchet permits meansto be later described to open the switch 13 and break the circuit withwhich the device is used.

The heating element 25 is preferably formed of iron wire as iron has apositive temperature coefficient and its resistance when heatedincreases so that the device is quickly brought to a temperature atwhich the solder melts to permit opening or the switch 13.

The upper part 12 of the bracket is apertured in axial alignment withthe threaded aperture- 23 of part 10 and that portion adjacent .the aperture is reduced in width to form shoulders 39 extending to each side ofthe frame as best illus-,

trated in Figure 2. A stud 40 having a bearing portion 41 is secured inthe aperture of the part 12 oi the bracket by a nut 42 and the bearingportion 41 thereof extends below the bracket part mounted thereon by a,stud '4'6. The'roller en- 12 and through a bushing 43' on a switch armactuating lever 43 to medially pivotally mount the lever, the inner arm44 thereof being provided with a roller 45 of insulating material-p'ivotally gages the switch arm 13 to maintain the same inits closedposition.

The outer arm 4'7 01 the lever 43 has a stud 43 secured thereto at'apoint spaced from its pivotal mounting'4l to provide means for mountinga pawl 49, the pawl having a bushing secured thereto in which the stud431s positioned.

The pawl 49 is arranged to engage the teeth of the ratchet 35 and isyieldably urged to such engagement by a pawl spring 51 having one endengaging the outer edge of the pawl and being medially coiled about thebushing 50 and having its other end engaging a stop 52 extendeddownwardly from the arm 4'7. Thus, as the arm 47 is swung about itspivot 41 to move the roller 45 into engagement with the switch arm 13 toclose the contacts 14 and 19, the pawl 49 moves over the teeth of theratchet 35 and engages the tooth nearest its limit of movement tomaintain the parts in said adjusted position as long as the currentflowing through the circuit with which the device is used is within apredetermined value.

A spring 53, having its medial portion coiled about the bushing 43 ofthe lever 43 and having one end 54 hooked behind one shoulder 39 of thepart 12 of the bracket with its other end 55 engaging the bushing 50,normally yieldably urges the lever 43 toward inactive position, tend- 4ing at all times to produce rotation of the ratchet 35 on the stem 34 topermit the roller 45 to move away from the switch arm 13, to a positionillustrated in dotted lines in Figure'3.

As long as the circuit is operating under normal conditions the partsmaintain their operative positions but when an over-load occurs, theheating element 25 heats the stem 34 to melt the solder and thus freespring 53 to turn the ratchet 35 and permit the lever 43 to assume itsdotted line position shown in Figure 3, breaking the circuitat thecontacts 14 and 19. As the circuit is thus broken, the element 25quickly cools and the solder again sets and secures the ratchet 35 tothe stem 34. Resetting of the device is then accomplished by moving thearm 47 of lever 43 to move the switch arm 13. toits closed position 1where it is held by the engagement of the pawl 39 with one of the teethoi! the ratchet 35.

s A cover 56 suitably secured to the housing completely encloses. thedevice and a resetting lever 5'7 having a stud 58 extending outwardlythrough the cover and with an actuatingknob 59 positioned thereonprovides means for moving the arm 4'! of the lever '43 to the right withrespect to Figure 2 to reset the mechanism. The arm 57 is normally heldin its inactive position by a spring 60 coiled about the stud 58 andhaving one and engaging a projection 61 carried by the arm.

In Figure 5 is illustrated diagrammatically a simple motor circuit inwhich the over-load relay 1 described is incorporated. This circuitincludes the lead 18, terminal 1'1, switch arm 13, and its adapted to beengaged with the switch arms 68,

67 and 68 of a magnetically actuated switch 89 to close the circuit ofits motor "M" through conductors 70, 71 and 72. The heating elements 25in this instance are inserted in series with the I conductor and theconductor 72. v

The. switch 69 is closed by energization of a solenoid coil 73, thecircuit of which extends from the lead-in conductor 65, through aconductor 74 to a terminal '75, conductor 76 to one side of a startingswitch 7'1 from the other side thereof through a conductor '18 to oneside of a stopping switch '19 from the other side thereof through thelead 18 to terminal 17. From the terminal 17, the circuit continuesthrough the switch 13, contacts 14 and 19, through a conductor 80 to oneside of the solenoid coil '13, through the coil, through a conductor 81,through the second switch 13, its contacts 14 and 19 and through aconductor 82 to the side 63 of the line.

Initial closing of the starting switch 77 energizes the coil 73 whichcloses the switch 69 thus bridging the control circuit at the contact 75through switch arm 83 which is connected with the far side of thestarting switch '17, by a conductor 84 thus maintaining the controlcircuit closed until manual opening thereof by actuation of the stoppingswitch 79 or by opening of the switch 13 of either over-load relay.

From the foregoing description taken in connection with the accompanyingdrawings, it will be readily apparent to those skilled in the art towhich an invention of this character appertains that I provide anover-load relay which is simple in construction, which permits readyresetting thereof and one in which the heating element is' formed ofmaterial having a positive temperature coefllcient and in which theresistance thereof builds up as its heat increases.

What I claim as my invention is:

In an overloadrelay of the character described, a circuit closurenormally yieldably urgedto one position. a mounting member, an actuatingmember carried thereby and adapted to hold the circuit closure in itsother position, a tubular stem carried by said mounting member, alocking member on said tubular stem, thermally responsive means normallysecuring the locking member fixed to the stem, means connecting theactuating member with the locking member to normally maintain theactuating member in its position urging the circuit closure to saidother position, and a heating coil surrounding the stem whereby'anincrease in temperature of the coil is readily conducted to thethermally responsive meansv securing the locking member in fixedposition

